Root Cause Analysis

java.nio.file.FileSystemException

/usr/home/jenkins/jenkins-slave/workspace/Lucene-Solr-NightlyTests-5.x/lucene/build/core/test/J3/temp/lucene.index.TestDemoParallelLeafReader 78910BB799798171-001/tempDir-002/segs/6za9dzr2yvnqeaarom3jvpz6a_43/_0.fdt: Too many open files